Fluid catalytic cracking (FCC) is a vital process used in the refining of petroleum products. The majority of the refineries in use today utilize the FCC process. Fluid catalytic cracking is used to convert the high boiling, high molecular weight hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases and other petroleum products. The FCC process vaporizes and breaks the long-chain molecules of the high boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock at elevated temperatures and pressure in the presence of a catalyst, with the majority of the cracking occurring in the vapor phase. Feedstock is thereby converted into gasoline, distillate, and other liquid cracking products as well as lighter gaseous cracking products.
The cracking reactions produce carbonaceous material commonly known as coke, which deposits onto the catalyst. These coke deposits quickly reduce the catalyst's reactivity, requiring the catalyst to be regenerated. Regeneration is accomplished by burning off the coke which restores the catalyst activity. Fluid catalytic cracking can therefore be distinguished by three specific steps: the cracking step in which the hydrocarbons are converted into the lighter products, a stripping step to remove hydrocarbons absorbed on the catalyst, and a regeneration step to remove coke from the catalyst. The regenerated catalyst may then be reused in the cracking step.
FCC catalyst, both spent and regenerated, must be periodically sampled in order to monitor and track FCC unit performance. The sampling also allows the evaluation of the characteristics of the circulating equilibrium catalyst. The catalyst sampling information may be used: to adjust fresh catalyst and catalyst additive addition rates, to track the condition of the catalyst (activity, REO, surface area contaminants, etc.), or to monitor coke on the catalyst to track regenerator performance (note that this list is not intended to be an exhaustive list of the information which may be derived from catalyst samples).
Catalyst samples are typically extremely hot, often in the range of 800 to 1000° F. for spent catalyst and 1200 to 1400° F. for regenerated catalyst. Sampling catalyst often produces significant amounts of catalyst dust which can be extremely hot, and is a known skin and eye irritant. Further, catalyst sampling lines are prone to pluggage. These factors pose a risk to personnel taking the samples even when protected by the appropriate personal protective equipment (PPE).
The current method for obtaining a catalyst sample is a standard pipe, which is sloped at an angle in an attempt to minimize pluggage. The sampling pipe is directly attached to the FCC unit and, when activated, displaces catalyst sample into a desired container. Typically the catalyst is routed into a sample can which is placed in a basket in the top of a large drum, such as a 55 gallon drum known as a sampling drum. The sample can must be elevated to submerge the sample line into the sample can. This technique reduces catalyst contamination during the initial draw but it also limits the ability of the operator to monitor the flow and the level of catalyst in the sample can. Often the sample can over fills resulting in catalyst “splashing” which poses a risk to personnel taking the samples even when protected by the appropriate PPE. Further, if the sampling line is accidently disconnected from the sample can, hot catalyst is sprayed outward.
Removing the hot sample can from under the sample pipe presents another risk to the operator because the operator is exposed to the hot catalyst and the hot sample can. Once the catalyst sample is obtained, the sample line must be closed and purged with nitrogen. The current technique results in nitrogen being blown into the top of the collection drum which creates catalyst dust in the immediate area. Further, ambient conditions such as wind, rain or high heat can cause the catalyst dust to cover anything surrounding the sample can. Therefore, there exists a need for an improved and safer catalyst sampling method and apparatus which reduces catalyst dust, catalyst splashing, and user risk.